1. Field of the Invention
The present invention relates to an X-ray imaging apparatus which takes an image of an object such as a head of a human body along a desired tomographic plane.
2. Description of the Related Art
In the field of the dental diagnosis, conventionally, an X-ray panoramic imaging apparatus which takes a tomographic image along the curve of a dental arch is known as disclosed in, for example, Japanese Examined Patent Publication JP-B2 55-1053(1980). In such an X-ray panoramic imaging apparatus, an X-ray source and X-ray imaging means which is opposed to the X-ray source are moved along a desired locus, so that a curved-face tomographic image along the curve of the dental arch is obtained.
In the field of medical diagnosis, there is known an X-ray CT (computed tomographic) imaging apparatus which takes a tomographic image of an arbitrary site of a human body. In such an X-ray CT imaging apparatus, an X-ray source and X-ray imaging means which is opposed to the X-ray source are revolved in a predetermined direction, and an obtained image signal is processed by a computer, so that a CT image which is a section view at an arbitrary angle of an arbitrary site such as the head or the trunk can be obtained.
An X-ray panoramic imaging apparatus of the prior art is dedicated to the X-ray panoramic imaging, and hence can obtain only a panoramic tomographic image. The X-ray CT imaging apparatus of the prior art is used for taking a tomographic image of a large portion of the human body such as the head or the trunk, and dedicated to the CT imaging, with the result that it can obtain only a CT image.
In the field of dental diagnosis, if data such as the thickness of the jawbone are previously known prior to an implant operation or the like, the operation can be easily performed. Therefore, it is requested to take a partial CT image of the site to be subjected to the implant operation, by using an X-ray CT imaging apparatus. However, an X-ray panoramic imaging apparatus cannot take a CT image of such a site. An X-ray CT imaging apparatus of the prior art is bulky and expensive, and has a problem that the exposure dose is large. When the exposure dose is large during an imaging process, the allowable number of imaging processes is restricted. Such restriction may adversely affect the diagnosis.
When an X-ray CT imaging apparatus which is entirely independent from an X-ray panoramic imaging apparatus is used, the space for installing the X-ray CT imaging apparatus is problematic.
Recently, an X-ray imaging apparatus which can conduct both the X-ray panoramic imaging and the flat tomographic imaging is proposed (Japanese Unexamined Patent Publication JP-A 7-136158(1995)). In the apparatus, however, the flat tomographic plane must be determined before the imaging process, and the tomographic plane cannot be changed after the imaging process. Furthermore, the apparatus cannot obtain an image of a tomographic plane which intersects with the flat tomographic plane.
When the X-ray imaging is to be conducted, particularly, when the X-ray CT imaging is to be conducted on a local site, it is important to hold the site to be imaged of the object, an X-ray source, and X-ray imaging means in predetermined positional relationships. If they fail to be held in the predetermined positional relationships, a satisfactory X-ray image cannot be obtained.